The present invention generally relates to machine tools, and more particularly to a tool holder including an elastomeric drive dampener for eliminating harmonic resonance and preventing slippage between the tool holder and machine tool spindle.
As is well known, various tool holders have been utilized in the prior art which interface with a rotating spindle of a machine such as a milling or boring machine. These tool holders securely hold a cutting tool upon the machine during the cutting of a work piece. In most prior art tool holders, a central aperture is formed therein for receiving the shank portion of the cutting tool which is to be interfaced to the milling or other machine. Subsequent to the insertion of the shank portion of the cutting tool into the central aperture, the tool holder is drawn or pulled tightly into the spindle so as to rigidly maintain the cutting tool within the tool holder. Typically, the spindle of the machine tool includes a series of drive lugs disposed circumferentially about the spindle. The drive lugs mate with a series of lug recesses formed within the tool holder when the tool holder is drawn into the spindle. The drive lugs prevent slippage between the tool holder and the spindle during rotation of the machine tool.
Though interfacing the cutting tool to the machine, the prior art tool holders possess certain deficiencies which detract from their overall utility. In particular, when the elongate, extended shank of a long reach cutting tool is inserted into and secured within the central aperture of the tool holder, there is a tendency for a harmonic resonance to be generated through the cutting tool and into the tool holder, particularly when the cutting tool is used in a high speed milling application. Additionally, the drive lugs formed on the spindle and the lug recesses formed on the tool holder may not be perfectly positioned and balanced, thereby additionally giving rise to a harmonic resonance. Transfer of the harmonic resonance into the tool holder gives rise to slight movements thereof relative to the spindle, and in extreme cases results in the tool holder loosening within the spindle. As will be recognized, the resonance of the tool holder relative to the spindle results in the cut in the work piece being substantially out of tolerance.
A further deficiency with the prior art tool holders is that the manner in which the shank portion of the cutting tool is secured within the central aperture of the tool holder often results in the non-concentric mounting of the cutting tool within the tool holder. Such non-concentric mounting is unacceptable in modern, high tolerance machining applications such as those performed on a vertical milling machine. The minor variations in concentricity can further lead to imbalance of the tool holder and cutting tool thereby frequently leading to catastrophic failure in the cutting operation.
The present invention addresses the deficiencies of prior art tool holders by providing a tool holder which includes a dampening drive member for eliminating the harmonic resonance which typically occurs when long reach, extended shank cutting tools are used in high speed milling applications. Additionally, the present invention provides a tool holder that eliminates the use of locking lugs and recesses on the spindle and tool holder thereby reducing harmonic resonance occurring from such. In the tool holder constructed in accordance with the present invention, the non-concentric mounting of the shank portion of the cutting tool within the tool holder is also substantially eliminated by heat shrinking the shank portion of the cutting tool within the tool holder.